1. Field of the Invention
The present invention relates to a novel type of MOS-type semiconductor power component, this component being generally called a discrete component although several such components may be provided on the same chip, and/or they can be associated with logic circuits provided on the same chip.
2. Discussion of the Related Art
FIGS. 1A and 1B show, as an example, a perspective view and a cross-section view of a conventional vertical power diode. This diode is formed from a substrate comprising a heavily-doped N-type region 1 (N+) and a lightly-doped N-type region 2 coated with a P-type layer 3. The upper surface is coated with an anode metallization 4 and the lower surface is coated with a cathode metallization 5. Reference numeral 6 designates an insulating layer.
FIG. 2 is a perspective view of a vertical power thyristor. The thyristor includes a lightly-doped N-type substrate 10. On the upper surface side is formed a P-type well 11 containing an N-type cathode region 12. On the lower surface side is formed a P-type anode layer 13. An anode metallization MA, a cathode metallization MK, and a gate metallization MG are also provided. To avoid for the anode metallization to short-circuit substrate 10, or to separate this thyristor from a neighboring component, a peripheral P-type insulating wall 15 is generally provided.
A disadvantage of vertical components is their on-state resistance. Indeed, the thicknesses of the various layers and regions are optimized according to the desired diode characteristics. In particular, the thickness of N-type layer 2 (diode) or 10 (thyristor) must be sufficiently high for the component to have a desired breakdown voltage but must also be as small as possible to limit the on-state resistance of the component. In the case of a diode, N+ layer 1 has no active function in the diode operation. It is only used to ensure an ohmic contact with the metallization and is used to reduce the diode's on-state resistance linked to the fact that a silicon wafer has, in current technologies, a thickness of from 300 to 500 μm, in most cases much greater than the desired thickness of N layer 2 (for example, 60 μm to hold 600 V). In the case of the thyristor, the thickness of layer 10 is also imposed by the thickness of the silicon wafer and various means, often complex, are used to reduce it.
Another disadvantage of vertical components is that the surface area of the active junctions is linked to the surface area of the semiconductor chip taken up by the components, the junctions being horizontal (in planes parallel to the main diode surfaces).
Further, such components intended to handle high voltages pose many problems to ensure a proper breakdown voltage at the periphery of the semiconductor or Schottky junction, as well as to isolate the entire component and ensure its protection (insulating wall).
A PNN+ diode and a thyristor have been described as an example only, the problems indicated hereabove generally relating to vertical power or high-voltage components, for example, Schottky diodes, bi-directional components, or MOS-type voltage-controlled components.